1. Field of the Invention
The present invention relates to wireless communications. More particularly, the invention concerns a method and apparatus for predicting power control requirements for a supplemental channel used in conjunction with a fundamental channel.
2. Description of the Related Art
Traditionally, wireless communication systems were required to support a variety of services. One such communication system is a code division multiple access (CDMA) system which conforms to the xe2x80x9cTIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,xe2x80x9d hereinafter referred to as IS-95. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d and U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d both assigned to the assignee of the present invention, and co-pending U.S. patent application Ser. No. 09/382,438, entitled xe2x80x9cMETHOD AND APPARATUS USING A MULTI-CARRIER FORWARD LINK IN A WIRELESS COMMUNICATION SYSTEM,xe2x80x9d each of which is incorporated by reference herein.
More recently, wireless systems such as the CDMA systems mentioned above have offered hybrid services, such as providing both wireless voice and data communications. To coordinate the implementation of such services, the International Telecommunications Union requested the submission of proposed standards for providing high-rate data and high-quality speech services over wireless communication channels.
In a CDMA system, a user communicates with the network through one or more base stations. For example, a user on a remote station (RS) may communicate with a land-based data source, such as the Internet, by transmitting data to a base station (BS) via a wireless link. This link between the RS and the BS is commonly referred to as the xe2x80x9creverse link.xe2x80x9d The BS receives the data and routes it through a base station controller (BSC) to the land-based data network. When data is transmitted from the BS to the RS, it is transmitted on the xe2x80x9cforward link.xe2x80x9d In CDMA IS-95 systems, the forward link (FL) and the reverse link (RL) are allocated to separate frequencies.
The remote station communicates with at least one base station during a communication. However, CDMA RSs are also capable of communicating with multiple BSs simultaneously, such as during soft handoff. Soft handoff is a process of establishing a new forward and reverse link with a new base station before breaking the old links with the previous base station. Soft handoff minimizes the probability of dropped calls, that is, where a call is inadvertently disconnected from the system. A method and apparatus for providing communications between an RS and more than one BS during the soft handoff process is disclosed in U.S. Pat. No. 5,267,261, entitled xe2x80x9cMOBILE ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d assigned to the assignee of the present invention and incorporated by reference herein.
Given the growing demand for wireless data applications, the need for very efficient voice and data wireless communication systems has become increasingly significant. One method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled xe2x80x9cMETHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION,xe2x80x9d assigned to the assignee of the present invention and incorporated by reference herein. In accordance with the IS-95 standard, non-voice data or voice data is partitioned into code channel frames that are 20 msec wide with data rates as high as 14.4 Kbps.
A significant difference between voice services and data services is the fact that voice services have stringent fixed delay requirements. Typically, the overall one-way delay of voice services must be less than 100 msec. In contrast, selectively planned data service delays, even above 100 msec, can be used to optimize the efficiency of the communication system. For example, error correction coding techniques that require relatively long delays can be used with data service transmissions.
Some parameters that measure the quality and effectiveness of data transmissions are the transmission delay required for transferring a data packet, and the average throughput rate of the system. As explained above, a transmission delay does not have the same impact in data or xe2x80x9cnon-voicexe2x80x9d communication as it does for a voice or xe2x80x9cvoice-dataxe2x80x9d communication. Still, delays cannot be ignored because they are an important metric for measuring the quality of the data communication system. The average throughput rate is reflective of the efficiency of the data transmission capability of the communication system.
Further, in a wireless communication system, capacity is maximized when the transmission energy for a signal is kept to a minimum value while satisfying the quality performance requirements for the signal. That is, the quality of transmitted voice-data or non-voice data cannot be significantly degraded when received. One measure of the quality of a received signal is the carrier-to-interference ratio (C/I) at the receiver. Thus, it is desirable to provide a transmission power control system that maintains a constant C/I at a receiver. Such a system is described in detail in U.S. Pat. No. 5,056,109, entitled xe2x80x9cMethod and Apparatus for Controlling Transmission Power in a CDMA Cellular Telephone System,xe2x80x9d assigned to the assignee of the present invention and incorporated by reference herein.
It is well known that in cellular systems the C/I of any given user is a function of the location of the RS within a coverage area. In order to maintain a given level of service, TDMA and FDMA systems resort to frequency reuse techniques, i.e. not all frequency channels and/or time slots are used in each base station. In a CDMA system, the same frequency channel allocation is reused in every cell of the system, thereby improving the overall efficiency. The C/I associated with an RS determines the information rate that can be supported on the forward link from the base station to the user""s RS. An exemplary system for transmitting high rate digital data in a wireless communication system is disclosed in co-pending U.S. patent application Ser. No. 6,574,211, issued Jan. 3, 2003, entitled xe2x80x9cMETHOD AND APPARATUS FOR HIGHER RATE PACKET DATA TRANSMISSION,xe2x80x9d assigned to the assignee of the present application and incorporated by reference herein.
Because the C/I associated with a RS determines the information rate that can be supported on the forward link, it is useful to know transmission information for each frequency channel used and historic C/I information. This information is commonly collected at the RS and messaged to the BS. But this messaging uses valuable system resources. What is needed is an invention that would eliminate such messaging requirements. Preferably, the BS transmission power levels on a first channel would be used to predict favorable slots for transmitting additional data on a second channel.
Broadly, the present invention solves a new technical challenge posed by the increasing demand for wireless communication services. The invention concerns a method and apparatus for selecting a favored transmission xe2x80x9cslotxe2x80x9d for non-voice data that is transmitted in conjunction with a voice-data communication. The slot, reflecting a desirable power level and transmission rate for the non-voice data, is selected based upon the transmission power levels for voice-data transmitted by a base station to a remote station.
In one embodiment, the invention may be implemented to provide a method for predicting a favored slot for transmitting non-voice data on a supplemental channel used in a wireless communication system. Generally, metrics reflecting the quality of voice-data signals sent by a base location are measured at a remote station. One or more of the metrics, or a value representing the quality of the received signal, is messaged from the remote station to the base location. If desirable, the base location may adjust the voice-data transmission power in consideration of the messages or values. Concurrently, the forward link voice-data transmission power levels are monitored at the base location. The voice-data is transmitted to the remote station using the first channel, more specifically referred to herein as a fundamental channel.
In one embodiment, a dynamic transmission power value is computed using various voice-data transmission power levels transmitted on the first channel. This value is then used to select a desired slot for transmitting additional data. This additional data is transmitted on a second channel such as a supplemental channel, shared or not shared, using a desired transmission power level and data rate for transmitting the additional data.
In another embodiment, the invention provides an article of manufacture containing digital information executable by a digital signal-processing device. In yet another embodiment, the invention yields an apparatus used to practice the methods of the invention. The apparatus may comprise a remote station and at least one base station that has, amongst other things, a transceiver used to communicate information signals to the remote station. Obviously, to receive signals, the remote station also includes a transceiver communicatively coupled to the base station, and possibly satellites where applicable. The apparatus will also include at least one digital data processing apparatus, such as a microprocessor or application specific integrated circuit (ASIC), that is communicatively coupled to the network or one of its component parts.
The invention provides its users with numerous advantages. One advantage is that it allows power control of a supplemental channel to be established based upon the base location transmitted power for voice-data. Another advantage is that the invention reduces system resource costs currently experienced by communication networks. These networks rely on messages received from a remote station regarding the quality of the supplemental channel signal as received at the remote station. Yet another advantage is that the invention allows a favorable transmission slot in any channel carrying non-voice data to be selected using historic base location transmission power levels for voice data. The invention also provides a number of other advantages and benefits that should become even more apparent after reviewing the following detailed descriptions of the invention.